My dear boys: "The Rover Boys on the River" is a complete story in itself, but forms the ninth volume of "The Rover Boys Series for Young Americans." Nine volumes! What a great number of tales to write about one set of characters! When I started the series I had in mind, as I have mentioned before, to write three, or possibly, four books. But the gratifying reception given to "The Rover Boys at School," soon made the publishers call for the second, third, and fourth volumes, and then came the others, and still the boys and girls do not seem to be satisfied. I am told there is a constant cry for "more! more!" and so I present this new Rover Boys story, which tells of the doings of Dick, Tom, and Sam and their friends during an outing on one of our great rivers, -an outing full of excitement and fun and with a touch of a rather unusual mystery. During the course of the tale some of the old enemies of the Rover Boys turn up, but our heroes know, as of old, how to take care of themselves; and all ends well. In placing this book into the hands of my young readers I wish once more to thank them for the cordial reception given the previous volumes. Many have written to me personally about them, and I have perused the letters with much satisfaction. I sincerely trust the present volume fulfills their every expectation.